Polarity effect on failure of Ni and Ni2Si contacts on Si

Abstract

Stability of contacts in shallow junction devices against high current density is a reliability issue for very large scale integration technology. We have observed a strong polarity effect on failure at nickel and nickel silicide contacts on both n- and p-type Si under high stress conditions. In a pair of cathode and anode contacts the Ni/n+-Si contact pair fails at the anode, while the Ni/p+-Si pair fails at the cathode. The Ni/Ni2Si/n+-Si and Ni/Ni2Si/p+-Si were found to fail preferentially at the cathode. Microbeam Rutherford backscattering spectrometry and Auger electron spectroscopy depth profiles show that a silicide reaction occurs between Ni and Si during current stressing, especially at the failed contacts. In situ resistance data indicate that the resistance of the failed contact increases with time while that of the other contact in the pair remains constant. Transmission electron microscopy shows that the silicide formation is not uniform at the damaged contacts. A mixture of dominant epitaxial NiSi2 and a minor amount of polycrystalline NiSi2 phases was identified. We have proposed mechanisms to explain the polarity effect on failure: wear-out mechanism for the damaged positive contacts of Ni/n+-Si, electromigration enhanced silicide formation for the damaged negative contacts of Ni/Ni2Si/n+-Si and electron-hole recombination mechanism for the damaged negative contacts of Ni/p+-Si and Ni/Ni2Si/p+-Si.

Current-Induced Degradation of Nickel Ohmic Contacts to SiC

“…The reliability of contacts to Si on the order of a micron or less utilizing various metallization schemes for integrated circuit (IC) technology has been studied. [1][2][3][4][5][6][7] The findings illustrate the potential for reactions and diffusion between the metals and the semiconductor, causing an increase in resistance, leading to thermal runaway, as well as the movement of material away from the contact interface, producing an open circuit. The degradation mechanisms varied depending on the metallization used.…”

Investigation of polarity effects on the degradation of Pd/Ti/Pt ohmic contacts to p-type SiC under current stress

“…Okojie et al has demonstrated contacts to n-type SiC with good thermal stability, including Ti=TiN=Pt contacts aged at 650 C for 65 h in air 10 and Ti=TaSi 2 =Pt contacts aged at 600 C for 1000 h in air, 11 as well as W-Ni alloy contacts to both n-type and p-type SiC annealed at 900 C for 1 h in Ar. Preferential degradation of either the anode or cathode has been observed in Ni and Ni 2 Si contacts to n-and p-type Si, 13 which is referred to as a polarity effect. The ohmic contact annealing a) Electronic mail: mohney@ems.psu.edu temperature, contact resistance, and surface morphology have been evaluated, as well as the stability of the contacts under continuous and pulsed dc lateral current stressing.…”